High frequency piezoelectric crystal composites, devices, and methods for manufacturing the same

ABSTRACT

The present invention generally relates to high frequency piezoelectric crystal composites, devices, and method for manufacturing the same. In adaptive embodiments an improved imaging device, particularly a medical imaging device or a distance imaging device, for high frequency (&gt;20 MHz) applications involving an imaging transducer assembly is coupled to a signal imagery processor. Additionally, the proposed invention presents a system for photolithography based micro-machined piezoelectric crystal composites and their uses resulting in improved performance parameters.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Prov. Ser. No. 61/344,801filed Oct. 13, 2010, the entire contents of which are incorporatedherein by reference.

FIGURE SELECTED FOR PUBLICATION

FIG. 3

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of piezoelectric crystals andpiezoelectric crystal composites operating for high frequency (>20 MHz).More particularly, the present invention provides high frequencypiezoelectric crystal composites for high resolution imagery forpreferred use in industrial and medical ultrasound applications, andeven more particularly to the methods of manufacturing the same.

2. Description of the Related Art

Conventionally, PMN-PT based piezoelectric single crystals have superiordielectric and piezoelectric properties compared to the traditional PZTceramics. To more fully exploit the excellent properties of singlecrystals, crystal composites have been fabricated to improve theelectromechanical coupling coefficient and thus transducer performancecharacteristics.

For ultrasound transducers, the operating frequency is inversely relatedto the thickness of the piezoelectric material. Thus, as the targetedoperating frequency increases, the thickness of piezoelectric materialdecreases accordingly this induces operative and electro mechanicaldifficulties. On the other hand, an optimal aspect ratio has beenattempted for the piezoelectric crystal pillars in order to maintain thehigh electromechanical coupling coefficient of piezoelectric composite.To accommodate the requirements in thickness and aspect ratio, thefeature size of the piezoelectric material in the high frequencycomposite needs to be reduced to meet the optimal ratio.

One attempt has been provided for such medical applications ofmicromachined imaging transducers known generally from U.S. Pat. No.7,622,853 (Rehrig et al., assigned to SciMed Life Systems, Inc.), theentire contents of which are incorporated herein by reference.

As noted in U.S. Pat. No. 7,622,853, a medial device is provided with atransducer assembly including a piezoelectric composite plate formedusing photolithography micromachining. The particular steps in the '853patent are noted therein. The '853 patent additionally notes theconventional challenges of micromachining poled PZT ceramics, but failsto adjust to the now appreciated challenges noted below and additionallyincludes the detrimental impacts of electric field and clamping effecton strain. There is now appreciated a need for further imageryresolution and sensitivity over a depth that cannot be achieved.

Finally, it is further recognized that a high frequency transducer istypically driven at a higher electrical field compared to a lowfrequency transducer.

Accordingly, there is a need for an improved high frequencypiezoelectric crystal composite, optionally related devices, and furtheroptionally methods for manufacturing the same.

Related publications include the following, the entire contents of eachof which are incorporated herein fully by reference:

-   1. P. Han, W. Yan, J. Tian, X, Huang, H. Pan, “Cut directions for    the optimization of piezoelectric coefficients of PMN-PT    ferroelectric crystals”, Applied Physics Letters, volume 86, Number    5 (2005).-   2. S. Wang, et al., “Deep Reactive Ion Etching of Lead Zirconate    Titanate Using Sulfur hexafluoride Gas”, J. Am. Ceram. Soc., 82(5)    1339-1341, 1999.-   3. A. M. Efremov, et al., “Etching Mechanism of Pb(Zr, Ti)O₃ Thin    Films in Cl₂/Ar Plasma”, Plasma Chemistry and Plasma Processing    2(1), pp. 13-29, March 2004.-   4. S. Subasinghe, A. Goyal, S. Tadigadapa, “High aspect ratio plasma    etching of bulk Lead Zirconate Titanate”, in Proc. SPIE—Int. Soc.    Opt. Engr, edited by Mary-Ann Maher, Harold D. Stewart, and    Jung-Chih Chiao (San Jose, Calif., 2006), pp. 61090D1-9.

ASPECTS AND SUMMARY OF THE INVENTION

In response, it is now recognized for the present invention thatimproved PMN-PT based piezoelectric crystal composites and for methodsfor manufacturing composite crystal elements required and are providedherein.

The present invention generally relates to high frequency piezoelectriccrystal composites, devices, and method for manufacturing the same. Inadaptive embodiments an improved imaging device, particularly a medicalimaging device or a distance imaging device, for high frequency (>20MHz) applications involving an imaging transducer assembly is coupled toa signal imagery processor. Additionally, the proposed inventionpresents a system for photolithography based micro-machinedpiezoelectric crystal composites and their uses resulting in improvedperformance parameters.

The present invention additionally relates to imagery devices,particularly medical devices and especially to improved medical imagingdevices and systems that employ the proposed novel structures of crystalcomposite and composite crystal elements.

It is a further aspect of the present invention that the innovativefabrication approaches make the commercial production of crystalcomposite feasible and practical. The high frequency crystal composite(20 MHz to >100 MHz, and a thickness electro-mechanical coupling factork_(t) 0.65-0.90 can be used for medical ultrasound imaging and diagnosiswith significantly improved performances. The high frequency crystalcomposite is especially applicable to use with skin, eye, intravascular,intracardiac, intracranial, intra-cavity or intra-luminal medicaldiagnosis devices. Such devices may be used in applications involvingdermatology, ophthalmology, laparoscopy, intracardiac and intravascularultrasound.

There is a further aspect of the invention that recognizes the use ofcrystal with a high coercive field (EC) when transducer excitation fieldis also high. In one alternative aspect of the present invention,ternary crystals Pb(In ½Nb½)O3-Pb(Mg⅓Nb⅔)O3-PbTiO3 (PIN-PMN-PT) andother PMN-PT based crystals are recognized as having improved thermaland electrical properties than the binary PMN-PT crystal. As aconsequence, an alternative embodiment of the invention employs acrystal composite based on these crystals which it is now recognizedinherit the improved properties of the ternary crystals.

In one aspect of the particular invention there is provided apiezoelectric PMN-PT based crystal composites, having the crystalcomposition represented by the formula I:x*Pb(B′1/2B″1/2)O3-y*PbTiO3-(1-x-y)*Pb(Mg1/3Nb2/3)O3, where, x isdefined as molar % 0.00 to 0.50; and y is defined as molar % 0.00 to0.50, B′ represents Indium (In), Ytterbium (Yb), Scandium (Sc) or Iron(Fe), B″ represents Niobium (Nb) or Tantalum (Ta). Additionally, formulaI be combined with additives Manganese (Mn) of up to 5% (wt %) and/orCerium (Ce) of up to 10% (wt %) of a total batch weight.

In one aspect of the particular invention there is provided apiezoelectric PMN-PT based crystal composites, having the crystalcomposition represented by the formula II:x*ABO3-y*PbTiO3-(1-x-y)*Pb(Mg1/3Nb2/3)O3, where, x is defined as molar %0.00 to 0.50; and y is defined as molar % 0.00 to 0.50, A representsLead (Pb) or Bismuth (Bi), B represents Indium (In), Ytterbium (Yb),Iron (Fe), Zirconium (Zr), Scandium (Sc), Niobium (Nb), Tantalum (Ta),or a combination of the above elements. Additionally, formula II may becombined with additives Manganese (Mn) of up to 5% (wt %) and/or Cerium(Ce) of up to 10% (wt %) of a total batch weight.

In a further aspect of the invention piezoelectric crystal compositeshaving formula I or II above are prepared by a method involvingphotolithograph based micromachining.

In a further aspect of the invention of the proposed invention as notedherein the composite posts proposed have an aspect ration of a postheight (H) to an effective post width (W), H:W, of greater than 0.50,preferably greater than 1.0, and more preferably greater than 2.0

In a further aspect of the invention the proposed composite is adiscontinuous hexagonal arrangement in a hybrid 1-3 configuration, andthe piezoelectric crystal is (001) cut and poled in <001> direction.

In a further aspect of the invention, the proposed composite is adiscontinuous hexagonal arrangement in a hybrid 1-3 configuration, andthe piezoelectric crystal is (011) cut and poled in <011> direction,wherein polymeric fill lines extend in)+/−32.5° (+/−2.5°) away from <101> direction.

In a further aspect of the invention, the proposed composite isparallelogram hybrid 2-2/1-3 configuration, and the piezoelectriccrystal is (011) cut and poled in <011> direction, wherein polymericfill lines extend in)+/−32.5° (+/−2.5°) away from <10 1> direction.

The above and other aspects, features, systems, methods, and advantagesof the present invention will become apparent to one with skill in theart upon study of the following description read in conjunction with theaccompanying drawings, in which like reference numerals designate thesame elements. It is intended that all such additional systems, methods,features, compositions, and details included within this description, bewithin the scope of the invention, and be protected by the accompanyingclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow for a photolithography based micro machiningprocess according to the present invention.

FIG. 2 is an illustrative schematic view of an imaging transducerarrangement operatively coupled with a digital transducer signalprocessor for operatively imaging the signals from the imagingtransducer.

FIG. 3 is a 2-dimensional plot for calculated value of d₃₁ on (011)plane (the plane out of the paper) for a PMN-PT crystal. FIG. 3indicates that the micro strain is fully zero in the directions +/−32.5°(see arrows) between curves. Calculated using formulad′₃₁=d₃₁*Cos(θ)*Cos(θ)+d₃₂*Sin(θ)*Sin(θ).

FIG. 4A is an illustrative perspective schematic of a hybrid 1-3 crystalcomposite for a transducer having a hexagonal structure, <001> cut,noting directional orientation and epoxy polymer and crystaldesignations with no impact on clamping direction due to <001> cut.

FIG. 4B it a top-view SEM image of a 1-3 crystal composite of FIG. 4Afor a transducer having a hexagonal structure, <001> cut, thickness 30μm, wherein the black lines are understood as kerfs filled with an epoxypolymer, in accordance with a preferred embodiment of the presentinvention.

FIG. 5A is an illustrative perspective schematic of a 1-3 crystalcomposite for a transducer having a hexagonal structure, <011> cut,noting directional orientation and epoxy polymer and crystaldesignations

FIG. 5B is a top-view SEM image of a hybrid 1-3 crystal composite ofFIG. 5A for a transducer having a hexagonal structure, <011> cut,thickness 22 μm, wherein the black lines are kerfs filled with an epoxypolymer, in accordance with a preferred embodiment of the presentinvention.

FIG. 5C is an illustrative orientation drawing noting the kerforientation at the identified 30°, and a clamping direction between 30°and 35°, and preferably +/−32.5° from the <10 1> direction orientationfor a hexagonal polygon arrangement as in FIGS. 5A and 5B.

FIG. 5D is an illustrative dimensioning guide regarding calculatingeffective post widths where not square, here, an average width iscalculated from the diagonal widths and heights for aspect ratioconsiderations.

FIG. 6A is an illustrative perspective schematic of a 1-3 crystalcomposite for a transducer having a parallelogram (diamond) structure,to minimize the transverse clamping effect by the epoxy polymer filledkerfs, in accordance with a preferred embodiment of the presentinvention.

FIG. 6B is an illustrative plan view in (011) cut of a hybrid 1-3crystal composite (of FIG. 6A) for a higher coupling factor wherein thetransverse epoxy polymer filled kerfs are made at +/−32.5° (+/−2.5°) aretherefore strain free. The clamping effect direction is noted.

FIG. 7A is a schematic pattern drawing of the proposed hybrid 2-2/1-3crystal composite of an (011) cut with the kerf filling line in thedirection of +/− 32.5° (+/−2.5°) relative to the <10 1> direction.

FIG. 7B is a top-view SEM image of an (011) cut hybrid 2-2/1-3 crystalcomposite as in FIG. 7A, in accordance with a preferred embodiment ofthe present invention.

FIG. 7C is a perspective view of FIG. 7A showing a schematic patterndrawing of the proposed hybrid 2-2/1-3 crystal composite of an (011) cutwith the kerf filling line in the direction of)+/−32.5° (+/−2.5°)relative to the <10 1> direction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to embodiments of the invention.Wherever possible, same or similar reference numerals are used in thedrawings and the description to refer to the same or like parts orsteps. The drawings are in simplified form and are not to precise scale.For purposes of convenience and clarity only, directional (up/down,etc.) or motional (forward/back, etc.) terms may be used with respect tothe drawings. These and similar directional terms should not beconstrued to limit the scope of the invention in any manner.

As will be used herein the Miller Indices identifiers serve as vectorrepresentations for orientation of an atomic plane in a crystal latticehaving three axes represented by a set of 3 integer numbers, for examplesuch conventional identifiers as, for example <010> or <10 1>, are used.

As will be further used herein, for example regarding the images of thepresent invention wherein polymeric (epoxy) regions are filled with apiezoelectrically non-active material, that the use of the phrase “kerf”is not limited to a region formed by a mechanical saw of anykind—instead the phrase “kerf” will be understood broadly by onesskilled in the art to represent the region between piezoelectric postswhich receiving polymeric material, whether or not the actual region isformed by a saw, or by any other manufacturing process discussed herein.

Additionally, a description methodology (the M-N labeling convention) isused to describe the number of directions which each section of thepiezoelectric material and polymeric material continuously extend,wherein M represents the number of continuous directions in which thepiezoelectric (PMN-PT) material extends and N represents the number ofdirections in which the polymeric (epoxy) material continuously extends.While those of skill understand this convention, however as modifiedherein, the structures suggested herein have never been subjected to theM-N convention and therefore applicant requires a hybrid understandingwherein the directional extensions generally remain, but arediscontinuous or interrupted, for example, by intersection with a crossdirectional polymeric material extending in a different and alsodiscontinuous direction. In this manner, it will be understood that the(as later described) hexagonal structure involves discontinuous,interrupted, or hybrid polymeric (epoxy) material directions where thepolymeric material direction is linear in only one direction along thelength of the piezoelectric material itself and the other polymeric(epoxy) directions are interrupted-in-direction ordiscontinuous-in-direction by encountering piezoelectric material. Oneembodiment of the invention further has a structure the result of thepiezoelectric material elements having discontinuous or interrupted sidealignments with respective sides/edges of proximate piezoelectricmaterial elements, so that sides/edges may not be coplanar (on the sameplane) but may extend on parallel planes. Still a further embodiment ofthe invention does not contain simple regular unit elements (FIGS. 7A-7Cfor example), and instead requires a still further hybridization of theM-N convention.

This invention relates to the 20 MHz to >100 MHz high frequencypiezoelectric single crystal composites/composite crystal elements andthe process for the preparation thereof. The novel high-coupling factorcrystal composites can broadly replace the legacy materials such aspiezoelectric ceramics, single crystal and traditional crystal compositefor high frequency transducers.

Referring now to FIG. 1 a process flow for a photolithography basedmicro machining process 100 is discussed. In the first step 10, a plateor block of piezoelectric single-crystal material (shown later), such asPMN-PT (Lead Magnesium Niobate-Lead Titanate) based crystals, such asbinary solid solution PMN-PT and ternary solid solution PIN-PMN-PT (LeadIndium Niobate-Lead Magnesium Niobate-Lead Titanate) or PYbN-PMN-PT(Lead Ytterbium Niobate-Lead Magnesium Niobate-Lead Titanate) or thesecrystals above with dopants (Mn, Ce, Zr, Fe, Yb, In, Sc, Nb, Ta, andothers). Such ternary crystals of the PMN-PT based piezoelectriccrystals are now recognized as having improved thermal stability andincreased coercive field that allows a higher driving electrical field.

The crystal composite and the composite crystal elements have novelstructures and/or new crystallographic cut directions. The crystalcomposites can be fabricated by proprietary procedures includingphotolithography, deep reactive ion etching, fine mechanical finishingand electrode coating.

The plate (not shown) is preferably lapped on both sides and polished onone of the sides. The lapped and unpolished side can then be bonded to aglass carrier (not shown), which is bonded to a silicon, Si, wafer (notshown). The dimensions of the plate are in the range of ten (10)millimeters (“mm”)×ten (10) mm×0.20 mm-to-1.20 mm in thickness; however,the dimensions could be of any size.

The material of the plate is a single crystal with electroded facesoriented along the <001> or <011> crystallographic directions. As one ofordinary skill in the art would appreciate, a single crystal structurecan desirably have a high piezoelectric coefficient (e.g., d₃₃>2000pC/N, d₃₃>0.8, d₃₃′>0.7). The plate preferably has a dielectric constantin the range of approximately 4000 to >7700 and a dielectric loss ofless than 0.01.

It will be recognized that the plate piezoelectric single crystal is aternary crystal formed according to the following formulas I or II:

Formula I: x*Pb(B′1/2B″1/2)O3-y*PbTiO3-(1-x-y)*Pb(Mg1/3Nb2/3)O3, where,x is defined as molar % 0.00 to 0.50; and y is defined as molar % 0.00to 0.50, B′ represents Indium (In), Ytterbium (Yb), Scandium (Sc) orIron (Fe), B″ represents Niobium (Nb) or Tantalum (Ta). Additionally,formula I may be combined with additives Manganese (Mn) of up to 5% (wt%) and/or Cerium (Ce) of up to 10% (wt %) of a total batch weight.

Formula II: x*ABO3-y*PbTiO3-(1-x-y)*Pb(Mg1/3Nb2/3)O3, where, x isdefined as molar % 0.00 to 0.50; and y is defined as molar % 0.00 to0.50, A represents Lead (Pb) or Bismuth (Bi), B represents Indium (In),Ytterbium (Yb), Iron (Fe), Zirconium (Zr), Scandium (Sc), Niobium (Nb),Tantalum (Ta), or a combination of the above elements. Additionally,formula II may be combined with additives Manganese (Mn) of up to 5% (wt%) and/or Cerium (Ce) of up to 10% (wt %) of a total batch weight.

Several non-limited examples of formulae I and II are found in thefollowing table. It will be recognized that any composition matching theformulae I or II is included herein by reference as a suitablecomposition.

Formula I Formula II Example 1 31% PIN-46.7% 15% BiScO-58.6% PMN-26.4%PT PMN-20.8% PT Example 2 15% PIN-53.7% 15% BiScO-57.6% PMN- PMN-22.4%PT:8.9% 26.4% PT:1% Ce Ce Example 3 25% PYbN-45.7% 10% BiScO-58.6% PMN-PMN-25% PT:2% Mn 26.4% PT:5% Mn Example 4 10% PZrT-64% 7% BaTiOs-61%PMN-PT-32% PT PMN-24% PT:3% Mn

In a second step 20 of photolithography a thin metal (Nickel) seed layerwas applied and then in a step 30 a mask was prepared by spincoating aphotoresist on top of the seed layer. The mask defines the desired shapeand/or pattern of imaging element(s) within the piezoelectric compositematerial. After baking, UV exposure, and development, a patternedphotoresist was obtained.

A Nickel mask of a predetermined thickness (here 10 microns, but can beany thickness from 1 to 30 microns) was electroplated thereon to havethe inverse pattern of the mask of the photoresist, which was thenstripped away using reactive ion etching. The use of hard or highmolecular weight metals such as Ni and Pt, is desirable for selectivityto protect the covered underlying area of the plate from being lateretched.

The etching process, such as reactive ion etching (“RIE”) is used asnoted, but other etching processes can be used, such as wet-etching. Inone preferred embodiment, chlorine, Cl₂ based RIE etching is used, whichhas an etching rate of approximately from less than 3 microns/hour to 12microns/hour and can cause a substantially vertical etching profile(e.g., >89 degree.). In the alternative, or in addition, to Cl₂, sulfurhexafluoride, SF₆, based etching can be used, which has similar etchingproperties to that of Cl₂. The nickel, Ni, pattern protects theunderlying portions of the plate covered by the pattern from the etchingprocess.

In a step 40 the crystal parts with the patterned etched mask werelocated into an ICP-plasma unit for deep reactive ion etching (DIRE)using the preferred Cl₂ gas. As a result of step 40, one or more deepposts of the type discussed later are formed in the plate with one ormore kerfs bounding each respective post, etched in the uncoveredportions of the plate. The one or more kerfs can have a width in therange of approximately from less than one (<1) to twelve (12) microns,and preferably from 1 to 10 microns in width.

The respective posts can have a width ranging from approximately 3 to200 (or longer in length for the hybrid 2-2/1-3 configuration discussedherein) microns and have a height in the range of approximately lessthan five (<5) to more than seventy (>70) microns, such that in oneembodiment, it is preferable to have an aspect ratio (post height/postwidth) of at least one to dampen the effect of lateral modes. For thedimensions of the plate described above, the etching process can lastapproximately six (6) to eight or eighteen (8 or 8) hours. After theetching step 40, the plate is then rinsed with a solvent for cleaning.

In the next step 50, the kerfs are filled with an epoxy, such as Epoxy301 provided by Epo-Tek, although other epoxies may be employed withoutdeparting from the scope and spirit of the present invention. A vacuum(not shown) may be utilized to remove air bubbles and prevent any voidwithin the kerfs. In the next step 60, after the epoxy cures, the topportion of the plate and epoxy are lapped to a thickness ofapproximately 25 microns. In a step 70, an electrode pattern is thenapplied to the plate to form the imaging transducer pattern. Theelectrode pattern is preferably comprised of gold (Au) and/or chromium(Cr). Moreover, as one of ordinary skill in the art would appreciate,electronic circuitry, such as imaging processing circuitry, (not shown)can be bonded to the electrodes (not shown). Further, the electrodepattern formed on the plate can define any pattern of imagingtransducers, including an array, e.g., an imaging transducer at eachpost, or a single imaging transducer. An epoxy layer may be applied tothe back of the plate.

In a further step 80 the plate is dimensioned suitably as desired andthen poled at 50 VDC. In a step 90 key dielectric and piezoelectricproperties are measured and calculated with suitable equipment, forexample Agilent 4294A Precision Impedance Analyzer.

Imaging transducers having an operating frequency at above 20 MHz, e.g.,to >100 MHz, can be developed using photolithography basedmicromachining, such as the process 100 described above. The higherfrequency of operation increases the resolution and image depth of animaging transducer. Furthermore, the bandwidth of the imagingtransducer, particularly when single crystal PMN-PT is employed as thepiezoelectric, can be close to 100%, compared to only 70 to 80% for <20MHz transducers made with PZT ceramic.

The greater bandwidth improves the transducer's axial resolution, whichincreases the imaging depth. This is desirable for high frequencytransducers, which have very limited imaging depth due the strongattenuation of high frequency ultrasound in tissue. When single crystalis used, these advantages can be achieved with sensitivities equivalentto or better than ceramic transducers. These high frequency transducerscan be applied to a number of medical procedures including the imagingof the anterior region of an eye for monitoring surgical procedures suchas cataract treatment by lens replacement and laser in situkeratomileusis (LASIK) and tumor detection (preferably up to sixty (60)MHz for fifty (50) .mu.m resolution); skin imaging for care of burnvictims and melanoma detection (preferably twenty five (25) MHz forsubcutaneous, fifty (50) MHz for dermis and one hundred plus (100+) MHzfor epidermis); intra-articular imaging for detection of pre-arthritisconditions (preferably twenty five (25) to fifty (50) MHz); in-vivomouse embryo imaging for medical research (preferably fifty (50) tosixty (60) MHz); Doppler ultrasound for determination of blood flow invessels<one hundred (100) .mu.m in diameter (preferably twenty (20) tosixty (60) MHz); intracardiac and intravascular imaging (preferably ten(10) to fifty (50) MHz); and ultrasound guidance for the biopsy oftissue.

As an example of such a medical device, we refer not to FIG. 2, whereinan exemplary medical treatment transducer device 200 includes an array(not shown) of transducers is joined with an exemplary array (not shown)of the proposed inventive piezoelectric posts (not shown) in a form(shown circularly) suitable for use in a catheter or guidewire of sometype. An exemplary guidewire and signal conduit 220 transmit receivedimagery signals to a computerized processing and imaging system 230 fordisplay of the received imaging signals. The conduit 220 may be formedin any conventional form operative for the purpose. For example it maybe formed of polymer or metal construction and contain multiple signalor control wires to operatively join a treatment end with the imagerydisplay comptroller.

The present inventors have determined that the PMN-PT basedpiezoelectric crystals usually use (001)-cut and poling <001> whichgives the highest d₃₃ but the lateral clamping effect by the epoxyfilled into kerfs cannot be avoided and his highly detrimental toperformance for a variety of imaging systems and methods of use. Wefirst use the hexagonal (“bee nest”) type hybrid shaped 1-3 type crystalcomposite. The advantage is significant in that the structure ismechanically much stronger and more stable than square-shaped pattern ifthe both piezo-effective volume is the same. It is much morepractical/suitable for large scale fabrication.

Referring now to FIG. 3, it was determined as particularly suitable the(011)-cut and poled PMN-PT based crystal for particularly high frequencytransducers. The advantage is the lateral clamping effect by the epoxyin kerfs can be totally avoided if the kerf filling in the direction of+7-32.50° (+/−2.5°) is used in a direction away from the <10 1>direction.

We have induced the formula (I) to calculate the d₃₁ by coordinationrotation:

d′ ₃₁ =d ₃₁*Cos(θ)*Cos(θ)+d ₃₂*Sin(θ)*Sin(θ)  (1)

From the 2-D plot of the d₃₁, it is indicated that the micro strains arezero in the +7-32.50° directions away from the <10 1> direction. It is asignificant advantage that the lateral strain-free arrangement willgreatly enhance the electromechanical coupling factor and broaden thebandwidth permissible in an ultrasound device.

Discussion of FIGS. 4A to 4B a schematic and SEM image of a hexagonalhybrid 1-3 crystal composite structure having an (001) cut. Here the‘hybrid’ phrase is used for M-N configuration as for the first timediscontinuous kerf lines are used and for the first time hexagonalcrystal posts are used. As a result, this aspect of the invention isisotropic, and the field/clamping effect is substantially the same inany direction since the kerf is parallel to the poling direction.Perspective view FIG. 4A illustrates directional orientation and hybridM-N arrangement for discontinuous or interrupted polymeric materialarrangements. The SEM image of FIG. 4B is shown having a thickness of 30microns. As noted, in view of the (001) cut and a poling at <001>direction, the clamping effect is substantially uniform in any direction(see illustrative arrows) and the reliability of the piezoelectriccrystal composite is greatly enhanced since failure direction must benon-linear and the clamping effect is also not directionally dependent.

Referring now to FIGS. 5A and 5B a schematic and SEM image of ahexagonal hybrid 1-3 crystal composite structure having a completely new(011) cut. Perspective view FIG. 5A illustrates directional orientationand hybrid M-N arrangement for discontinuous or interrupted polymericmaterial arrangements. Here the ‘hybrid’ phrase is used for M-Nconfiguration as for the first time discontinuous kerf lines are usedand for the first time hexagonal crystal posts are used, particularlynew with the (011) cut direction. The SEM image of FIG. 5B is shownhaving a thickness of 22 microns. As noted, in view of the (011) cut anda poling at <011> direction, the clamping direction is desirably 30-35°from <10 1> direction, and preferably about 32.5° (+/−2.5°) from the <101> direction. In this alternative embodiment, at least one kerf isguaranteed to be free of any clamping effect while the reliability ofthe piezoelectric crystal composite is greatly enhanced since failuredirection must be non-linear.

Referring now to FIG. 5C a schematic illustrative orientation drawingnoting the kerf orientation at the identified 30° from the <10 1>direction for the hexagonal hybrid 1-3 configuration, and a clampingdirection between 30° and 35°, and preferably +/−32.5° from the <10 1>direction, as noted in FIGS. 5A and 5B. It will also be recognized thatthe same 30° understanding off a designated direction is suitable forFIGS. 4A and 4B albeit from a different (001) cut direction.

Referring now to FIG. 5D, is an illustrative dimensioning guideregarding calculating effective post widths where not square, as here ina hybrid 1-3 configuration. As noted, either a hexagonal orparallelogram configuration designates a single height of thepiezoelectric crystal material and can be measured. Regarding each crosssectional view, there are multiple diagonals (either generally uniformas in the hexagon or non-uniform as in the parallelogram). On eitherconfiguration, multiple width measurements are taken and an average iscalculated for determination of an aspect ratio (Height:Width) ofpreferably greater than 0.50, more preferably greater than 1.0, and morepreferably greater than 1.5 or 2.0. However, each ideal ratio isdependent upon the other configurations, composition details, and deviceor method requirements. For example, one preferred alternativeembodiment includes a specific ratio of less than 2. As a furtherdetail, it will be noted (for example with the hybrid 2-2/1-3configuration of FIGS. 7A to 7C, that such aspect ratios are no longerapplicable. It will also be understood that typically a desired kerfwidth is between 1 micron to 10 microns.

As a result of preparing such composites according to the details hereinthroughout, a thickness electromechanical coupling factor k_(t) of0.65-0.90 is achieved.

Referring now to FIGS. 6A and 6B an alternative parallelogram hybrid 1-3configuration is presented with an (011) cut and a <011> polingdirection where the kerf lines run at 30-35° away from the <10 1> cut,and preferably at 32.5°+/−2.5°. This configuration minimizes thetransverse clamping effect by the epoxy filled into the kerfs betweenthe parallelogram shaped crystal posts. Based upon this hybrid 1-3configuration the composite crystal provides a high coupling factor,wherein the epoxy kerfs are transverse strain free. Here the ‘hybrid’phrase is used for M-N configuration as for the first time continuouskerf lines are used in a parallelogram pattern with the kerf lines being115° apart relative to a respective plane. This arrangement fullycancels the lateral clamping effect.

Referring now to FIGS. 7A to 7C. Here a schematic, SEM, and perspectiveview of a further discontinuous hybrid 2-2/1-3 configuration is providedwith repeated units shown, wherein the crystal is (011) cut and <011>poled. As graphically illustrated, the kerf filling line direction ispreferably 30-50° and more preferably 32.5°) (+/−2.5°) away from the <101> direction. As a result of this discontinuous hybrid 2-2/1-3configuration the clamping direction (shown) has no negative impact onperformance. It is noted that the white spaces in FIGS. 7A, 7C and theblack spaces in FIG. 7B represent epoxy or polymeric material, and thebars represent piezoelectric material. It is noted that the transverseextension strain is negative parallel to the <011> direction andpositive parallel to the <011> direction.

As noted herein with regards to FIGS. 7A to 7C, each individual unitmember (shown) is a unique geometry for smooth packing whilesimultaneously allowing for allowing gas outwardly during epoxyinfusion. Each unit member includes a central elongate web bar (shown)extending in a first direction from a first end to a second end.Respective bridge members or bridge portions (shown) extendperpendicularly from the elongate web bar on opposing sides (shown) andintermediate the respective first and second ends, forming a total offour bridge member parts, two on each side of the web bar (shown).Extending from each of the four bridge member parts are leg bars(shown), each leg bar parallel to the web bar and spaced therefrom by akerf width. In this configuration, it is thus understood that the hybrid2-2 configuration portion represents the parallel web bars and leg bars,each spaced by polymeric material, and the hybrid 1-3 configurationportion represents the interaction of the crossing bridge members andbridge member parts and the polymeric material cross-passages at the endof each leg bar. As a result, those skilled in the art will recognizethe hybrid 2-2/1-3 configuration as fully understood in conjunction withthe drawings.

It will be understood that the method of fabricating noted earlier maybe used to fabricate one of more imaging transducers having any of thehybrid configurations with any composition shown herein withoutdeparting from the scope of the entire disclosure. It will be understoodthat the compositions may be used in any configuration.

It will be understood that an imaging device may be configured asdiscussed in FIG. 2, and may be formed in any hybrid configuration inany composition shown herein without departing from the scope of theentire disclosure. It will be understood that the compositions may beused in any configuration.

It will be understood that the phrase hexagonal is a polygon with sixedges or sides in a plan view, such that the hexagonal polygons of thetype shown have six edges or sides and extend from an initial position.

It will be understood that there are many different kinds ofquadrilateral (four sided) polygons, and all have several things incommon: two opposing sides are coplanar, have two diagonals, and the sumof their four interior angles equals 360 degrees, however as notedherein, the phrase parallelogram used herein reflects two parallel pairsof opposite sides without right angles, and a rhombus is merely such aparallelogram with equal length sides (and may also be referred to as a‘diamond’ pattern or an oblique rhombus) with understanding by those ofskill in the art.

Having described at least one of the preferred embodiments of thepresent invention with reference to the accompanying drawings, it willbe apparent to those skills that the invention is not limited to thoseprecise embodiments, and that various modifications and variations canbe made in the presently disclosed system without departing from thescope or spirit of the invention. Thus, it is intended that the presentdisclosure cover modifications and variations of this disclosureprovided they come within the scope of the appended claims and theirequivalents. As a further example, each feature of one embodiment can bemixed and matched with other features shown in other embodiments, andsimilarly features may be added or removed such that the invention isrecognized as not restricted except in view of the appended claims.

What is claimed:
 1. A piezoelectric PMN-PT based crystal composite, saidpiezoelectric crystal composite having a crystal composition representedby the formula:x*Pb(B′_(1/2)B″_(1/2))O₃-y*PbTiO₃-(1-x-y)*Pb(Mg_(1/3)Nb_(2/3))O₃;wherein, x is defined as molar % 0.00 to 0.50; y is defined as molar %0.00 to 0.50; B′ represents Indium (In), Ytterbium (Yb), Scandium (Sc),Zirconium (Zr), or Iron (Fe); and B″ represents Niobium (Nb) or Tantalum(Ta).
 2. A piezoelectric crystal composite, according to claim 1, infurther combination with: an additive, said additive being selected fromthe group consisting of: Manganese (Mn) of up to 5% (wt %) and Cerium(Ce) of up to 10% (wt %) of a total batch weight.
 3. A piezoelectriccrystal composite, according to claim 1, wherein: said crystal compositehas a thickness electromechanical coupling factor k_(t) of about 0.65 to0.90.
 4. A piezoelectric crystal composite, according to claim 1,wherein: said crystal composite is operative at a frequency of at least20 MHz.
 5. A piezoelectric crystal composite, according to claim 1,wherein: said crystal composite is operative at a frequency of at least80 MHz.
 6. A piezoelectric crystal composite, according to claim 1, infurther combination with: a medical imaging device configured foroperative ultrasound imaging.
 7. A piezoelectric crystal composite,according to claim 1, wherein: said crystal composite is (011) cut and<011> poled and provides zero strain in the direction of +/−32.5°(+/−2.5°) away from the <011> direction according to the coordinaterotation d₃₁ formula:d′ ₃₁ =d ₃₁*Cos(θ)*Cos(θ)+d ₃₂*Sin(θ)*Sin(θ).
 8. A piezoelectric PMN-PTbased crystal composite, said piezoelectric crystal composite having acrystal composition with one lead-free component, and being representedby the formula:x*ABO₃-y*PbTiO₃-(1-x-y)*Pb(Mg_(1/3)Nb_(2/3))O₃; wherein, x is defined asmolar % 0.00 to 0.50; y is defined as molar % 0.00 to 0.50; A representsBismuth (Bi) or Barium (Ba); B represents one selected from the groupconsisting of: Indium (In), Ytterbium (Yb), Iron (Fe), Zirconium (Zr),Scandium (Sc), Niobium (Nb), Tantalum (Ta), and a combination of theseelements.
 9. A piezoelectric crystal composite, according to claim 8, infurther combination with: an additive, said additive being selected fromthe group consisting of: Manganese (Mn) of up to 5% (wt %) and Cerium(Ce) of up to 10% (wt %) of a total batch weight.
 10. A piezoelectriccrystal composite, according to claim 9, wherein: said crystal compositehas a thickness electromechanical coupling factor k_(t) of about 0.65 to0.90.
 11. A piezoelectric crystal composite, according to claim 8,wherein: said crystal composite is operative at a frequency of at least20 MHz.
 12. A piezoelectric crystal composite, according to claim 8,wherein: said crystal composite is operative at a frequency of at least80 MHz.
 13. A piezoelectric crystal composite, according to claim 8, infurther combination with: a medical imaging device configured foroperative ultrasound imaging.
 14. A piezoelectric crystal composite,according to claim 8, wherein: said crystal composite is (011) cut and<011> poled and provides zero strain in the direction of +/−32.5°(+/−2.5°) away from the <011> direction according to the coordinaterotation d₃₁ formula:d′ ₃₁ =d ₃₁*Cos(θ)*Cos(θ)+d ₃₂*Sin(θ)*Sin(θ).